There are many applications where it is important to quantify the extent of degradation that is or has occurred on a device. A metal surface which is exposed to a corrosive environment can experience at least two forms of corrosion. The first form of corrosion occurs relatively uniformly over the surface, and a second form is relatively localized. This localized form of attack is often described as pitting corrosion. Uniform corrosion can take a relatively long time to reduce the thickness of a body of material and mechanical strength. By contrast, pitting corrosion can lead to relatively rapid puncturing of a body of material which can more rapidly lead to part deterioration and loss of functionality.
Identification, counting, and accurately measuring geometric dimensions of corrosion-induced pits on metallic surfaces has been relatively challenging and time consuming. Available visual and non-visual techniques require manually focusing on individual pits, one pit at a time. Efficient techniques to identify, count, and measure geometric dimensions of pits are lacking, particularly for laboratory scale coupons ranging in dimensions up to few inches.
Metallic coupons are routinely used in corrosion experiments, in the laboratory and in the field, to characterize the effects of corrosion environments on materials of interest. If the material is susceptible to pitting corrosion in an environment under consideration, a variable number of pits develop on the coupon surface exposed to the environment. Quantifying the number of pits, the area and volume affected by pitting, the depth of individual pits, and the depth on the metal surface affected by pitting would be valuable to more efficiently characterize pitting corrosion and the severity of corrosive environments. While, as noted, it is possible to individually measure pits with microscopic techniques, these individual pit measurements are labor intensive, especially if there are numerous pits on a corrosion coupon. Furthermore, surface roughness of the coupon and its topography complicates accurate measurements of pits. An apparatus and method is needed to more efficiently characterize pitting corrosion while accounting for surface roughness and topography on laboratory scale coupons.